How can I set a maximum length or validation pattern in the tax type answers?

You can define a validation pattern or maximum length for tax questions by editing the SapTaxMetadataExport.csv file.

This can be done by following below steps:

1. Click Manage > Administration > Site Manager > Data Import/Export.
2. In the import/export section search for tax.
3. Click Export tab, then look for the Export Country-Specific Tax Fields task.
4. Click Export. This will generate the SapTaxMetadataExport.csv file.
5. The file exported will be the default pattern for all customers can modify the regex based on their ERP format.
6. Add the corresponding regex pattern for the countries and import the SapTaxMetadataExport.csv file.
   
   

The column that defines the validation pattern and/or maximum length is the RegexPattern.

More details regarding this topic can be found in Defining country/region-specific tax ID fields in Tax questions

Supplier Lifecycle & Performance > Bank/Tax/Ext Address